30 minutes ago, jetZeds said:
If the POI is "complex", you night have a hole that they are getting through that you aren't noticing. A good test is to generate heat or lure a zombie to your base and go inside and see if they find a way in or just attack walls. You may have to hit them if they attack walls to break them out of rage mode in case that is the reason they are hitting walls and not because they can't reach you.
Maybe also just double check your land claim boundaries, though since you have them visible in your screenshot, I assume you already did.